Number of found documents: 893
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NUMERICAL SUPPORT FOR STUDY OF STRESS RATIO EFFECT ON FATIGUE CRACK BEHAVIOUR IN THREE POINT BEND SPECIMEN MADE FROM VIBRATED CONCRETE
Seitl, Stanislav; Thienpont, T.
2016 - English
The fatigue behaviour of concrete has become more important for the design of structures due to more slender/slim structures, which are more sensitive to fatigue loading, or due to wind turbines, which are typically exposed to high-fatigue loading. The fatigue behaviour of concrete was investigated with respect to the influence of various stress ratios. Pilot analysis of fatigue crack propagation rate in three-point bend specimens made from ordinary vibrated concrete was done. Keywords: Stress intensity factor; fatigue crack; Paris-Erdogan law; concrete; FEM; stress ratio Available at various institutes of the ASCR
NUMERICAL SUPPORT FOR STUDY OF STRESS RATIO EFFECT ON FATIGUE CRACK BEHAVIOUR IN THREE POINT BEND SPECIMEN MADE FROM VIBRATED CONCRETE

The fatigue behaviour of concrete has become more important for the design of structures due to more slender/slim structures, which are more sensitive to fatigue loading, or due to wind turbines, ...

Seitl, Stanislav; Thienpont, T.
Ústav fyziky materiálů, 2016

Changes in structure and phase composition in the surface of tram rail
Švábenská, Eva; Roupcová, Pavla; Schneeweiss, Oldřich
2016 - English
We have investigated structure and phase composition of surface layer of tram rails after long time running and the results were compared with those obtained on the original part of material. Changes due to effects of severe plastic deformation together with thermal shocks by friction process were expected. The information about structure and phase composition was obtained by optical and scanning electron microscopy, X-Ray Powder Diffraction, Mössbauer Spectroscopy and Glow Discharge Emission Spectroscopy (GDOES) and this was completed by microhardness measurements. The results show that the surface layer in comparison with the original material exhibits important changes in grain structure, an increase in microhardness and high content of iron oxide and hydrooxides. According to the depth profile of the chemical composition measured by GDOES there is an increase in carbon content in the surface layer which can be effect of up-hill diffusion. Keywords: tram rail; microstructure analysis; surface Available at various institutes of the ASCR
Changes in structure and phase composition in the surface of tram rail

We have investigated structure and phase composition of surface layer of tram rails after long time running and the results were compared with those obtained on the original part of material. Changes ...

Švábenská, Eva; Roupcová, Pavla; Schneeweiss, Oldřich
Ústav fyziky materiálů, 2016

Fatigue crack growth in 316L under uniaxial and torsional loading
Karol, Michal; Chlupová, Alice; Mazánová, Veronika; Kruml, Tomáš
2016 - English
A study of fatigue crack initiation and growth in 316L austenitic stainless steel is reported. Fatigue experiments were performed at room temperature on full cylindrical specimens cycled axially (tension-compression) and on hollow cylindrical specimens tested in reversed torsion. Microstructure and damage evolution (crack initiation and growth) on the surface of mechanically and electrolytically polished specimens were observed using light and electron microscopy. An analysis of the orientation of microcracks and macrocracks which led to failure was made. Axially loaded specimens exhibited presence of several microcracks which resulted in macrocrack propagating perpendicularly to specimen axis. In the case of torsional loading, orientation of macrocrack propagation was dependent on applied load and presence of notches. High amount of short cracks initiated parallel to specimen axis. Long cracks exhibited a tendency to bifurcate with crack branches oriented at approximately 45° to the specimen axis. Keywords: 316L austenitic steel; surface relief; fatigue Available at various institutes of the ASCR
Fatigue crack growth in 316L under uniaxial and torsional loading

A study of fatigue crack initiation and growth in 316L austenitic stainless steel is reported. Fatigue experiments were performed at room temperature on full cylindrical specimens cycled axially ...

Karol, Michal; Chlupová, Alice; Mazánová, Veronika; Kruml, Tomáš
Ústav fyziky materiálů, 2016

HYDROGEN ABSORPTION IN A-Co30Fe55B15
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2016 - English
Hydrogen solved in amorphous alloys (AAs) influences their magnetic characteristics. AAs are also perspective\nas additives that can improve hydrogen storage kinetic in certain types of ball-milled hydrogen storage\nmaterials (HSMs). Therefore, knowledge of hydrogen solubility and hydrogen sorption kinetics in AAs are of a\ngreat importance for aimed design both AAs with optimal magnetic parameters and HSMs with desired sorption\ncharacteristics. In the present paper, amorphous alloy Co30Fe55B15 (an example of the type a-TM1xTM2y Bz ;\nTM - transition metal) was investigated. Hydrogen concentration c H was measured by Sieverts method in\ntemperature interval from T = 150 °C to T = 350 °C under hydrogen pressure p up to 6 MPa. It was found that\nc H was an increasing function of p and its maximum value was typically 0.5 wt.% H2 at 350 °C and 6 MPa.\nHowever, when the alloy was preliminary hydrogen charged (PHC), the pressure dependence of total c Htot in\nthe first absorption cycle(s) is non-monotonous in dependence on PHC conditions. For the sake of comparison,\nthe same absorption characteristics were measured also in Mg2Ni intermetallic that is a common constituent\nin Mg-based HSMs. Comparing Co30Fe55B15 and Mg2Ni, it was concluded that Co30Fe55B15 shows lower\nhydrogen solubility, but much better absorption kinetics. Keywords: absorption, Co 30 Fe 55 B 15; Hydrogen; Co30Fe55B15 Available at various institutes of the ASCR
HYDROGEN ABSORPTION IN A-Co30Fe55B15

Hydrogen solved in amorphous alloys (AAs) influences their magnetic characteristics. AAs are also perspective\nas additives that can improve hydrogen storage kinetic in certain types of ball-milled ...

Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
Ústav fyziky materiálů, 2016

INFLUENCE OF LASER CUTTING AND PUNCHING ON MAGNETIC PROPERTIES\nOF ELECTRICAL STEEL M470-50A
Bulín, Tomáš; Švábenská, Eva; Hapla, Miroslav; Ondrůšek, Č.; Schneeweiss, Oldřich
2016 - English
Electrical steel M470-50A belongs to the most often used materials in electrical machines. Due to this fact, it is desirable to know the magnetic parameters after processing raw sheets into the required shape. Basic parameters of mechanical, electrical, and magnetic properties of the sheets are usually obtained from the producer but the magnetic properties are changing in dependence on additional machining processes. The aim of this study is to describe changes in parameters of magnetic behavior after punching, laser and spark cutting of the original sheets. The basic information of structure was obtained by optical and scanning electron microscopy. The magnetic parameters were acquired from the measuring of magnetic hysteresis loops in dependence on saturation fields and frequencies. The results are discussed from the point of view of applied\ncutting technology with the aim to obtain the best magnetic parameters and consequently a higher efficiency of the final product. Results can be used as input parameters in simulation of the electrical machine. Keywords: magnetic properties; M470-50A steel; laser cutting; punching; spark cutting Available at various institutes of the ASCR
INFLUENCE OF LASER CUTTING AND PUNCHING ON MAGNETIC PROPERTIES\nOF ELECTRICAL STEEL M470-50A

Electrical steel M470-50A belongs to the most often used materials in electrical machines. Due to this fact, it is desirable to know the magnetic parameters after processing raw sheets into the ...

Bulín, Tomáš; Švábenská, Eva; Hapla, Miroslav; Ondrůšek, Č.; Schneeweiss, Oldřich
Ústav fyziky materiálů, 2016

HYDROGENATION PROPERTIES OF BALL-MILLED Mg-Ti-C-Zr COMPOSITE
Král, Lubomír; Čermák, Jiří; Roupcová, Pavla
2016 - English
The hydrogen storage properties of ball-milled Mg-Ti-Zr-C composite (1.8 wt.% Ti, 1.9 wt.% Zr and 0.2 wt.% C) were investigated. It has been previously shown, that the addition of Ti, Zr and C improved its storage properties. This beneficial effect of additives upon hydrogen storage properties can be explained by catalysis by the particles rich in Ti or Zr located on the surface of Mg grains. They provide effective pathways for the hydrogen diffusion into the MgH2. The morphological and microstructural characteristics were investigated by scanning electron microscopy and by X-ray diffraction. The hydrogen sorption was measured by Sieverts method using Setaram PCT-Pro device. In this paper, sorption behaviour of the composite after ball-milling and after aging on the air was compared. The ball-milled composite adsorbed 3.5 wt.% H2 within 10 min at 623 K. However, hydrogen storage capacity of the composite aged on the air for 7 months remarkably decreased: The aged composite adsorbed within 10 min only 2 wt.% H2 at 623 K and the sorption capacity decreased from 4.7 wt.% H2 to 2.1 wt.% H2. Keywords: hydrides; hydrogen storage; Mg-alloys Available at various institutes of the ASCR
HYDROGENATION PROPERTIES OF BALL-MILLED Mg-Ti-C-Zr COMPOSITE

The hydrogen storage properties of ball-milled Mg-Ti-Zr-C composite (1.8 wt.% Ti, 1.9 wt.% Zr and 0.2 wt.% C) were investigated. It has been previously shown, that the addition of Ti, Zr and C ...

Král, Lubomír; Čermák, Jiří; Roupcová, Pavla
Ústav fyziky materiálů, 2016

NUMERICAL SUPPORT FOR SPECIMEN LOADED BY BENDING AND WEDGE SPLITTING FORCES FOR MEASUREMENT OF CONCRETE PROPERTIES
Seitl, Stanislav; Liedo, R.; Holušová, T.
2016 - English
Fracture mechanical properties of silicate based materials are performed from various fracture mechanicals tests. For evaluation of parameters, the knowledge about calibration and compliance function is so important. Therefore, in contribution the compliance and calibration curves for a novel test based on combination wedge splitting test (WST) and three-point bend test (3PBT) are introduced. These selected variants exhibit significantly various stress state conditions at the crack tip, or, more generally, in the whole specimen ligament. Keywords: Stress intensity factor; T-stress, constraint; wedge splitting test; three-point bend test; compliance function; COD Available at various institutes of the ASCR
NUMERICAL SUPPORT FOR SPECIMEN LOADED BY BENDING AND WEDGE SPLITTING FORCES FOR MEASUREMENT OF CONCRETE PROPERTIES

Fracture mechanical properties of silicate based materials are performed from various fracture mechanicals tests. For evaluation of parameters, the knowledge about calibration and compliance function ...

Seitl, Stanislav; Liedo, R.; Holušová, T.
Ústav fyziky materiálů, 2016

Stress relaxation in partially pyrolysed SiOC materials
Halasová, Martina; Chlup, Zdeněk; Černý, Martin; Strachota, Adam; Dlouhý, Ivo
2015 - English
This paper focuses on the difficulty with Vickers hardness evaluation of SiOC materials. To evaluate it, diagonals of an indent are crucial. Due to stress relaxation in experimental material it was not possible to evaluate it in the whole range of experimental temperatures. As experimental materials were used two types of commercialy available polysiloxane resins, pyrolysed in range from 400 to 1000°C. Keywords: polysiloxane; resin; SiOC; glass; ceramics; Vickers hardness; 3D reconstruction; indent Available at various institutes of the ASCR
Stress relaxation in partially pyrolysed SiOC materials

This paper focuses on the difficulty with Vickers hardness evaluation of SiOC materials. To evaluate it, diagonals of an indent are crucial. Due to stress relaxation in experimental material it was ...

Halasová, Martina; Chlup, Zdeněk; Černý, Martin; Strachota, Adam; Dlouhý, Ivo
Ústav fyziky materiálů, 2015

Determination of mechanical properties of light alloys and composites by means of Small Punch Testing
Bártková, Denisa; Langer, J.; Dymáček, Petr; Válka, L.
2015 - English
Nowadays, in many testing areas a volume of experimental material is limited (laboratory-scaled volume, semidestructive approach). Therefore many testing techniques on miniature samples were devised. Principle of Small Punch Test (SPT) method is a penetration of small puncher through thin disc placed on a ring until the disc bursts. In dependence on loading mode it can provide information comparable to uniaxial tensile tests (UTT) and/or conventional constant load creep tests. However clarification of relations between SPT and conventional methods is difficult and empirical formulas are non-universal. The aim of this study is to i) evaluate mechanical properties of aluminium and magnesium alloys and its composites by means of SPT, ii) compare SPT results with UTT, iii) validate correlation formulas from literature, iv) propose more advanced approach to define correlation between UTT and SPT. Measurement were carried out at constant deflection rate (SPT-CDR) in two different laboratoires. Results from both laboratories were compared to evaluate the reproducibility of the method. Better results agreement was reached for the ultimate strength measurements. Yield strength results exhibited greater variance. An influence of pre-deformation of the sample on yield strength and deflection at maximum force was also identified. We can conclude, that for quantitative estimation of strength parameters we can use correlation formulas based on materials with similar composition and fracture behaviour. Keywords: Small Punch Test; Magnesium Alloys; Aluminium Alloys Thin Disc Available at various institutes of the ASCR
Determination of mechanical properties of light alloys and composites by means of Small Punch Testing

Nowadays, in many testing areas a volume of experimental material is limited (laboratory-scaled volume, semidestructive approach). Therefore many testing techniques on miniature samples were devised. ...

Bártková, Denisa; Langer, J.; Dymáček, Petr; Válka, L.
Ústav fyziky materiálů, 2015

Stress analysis of modified compact tension specimens: K-calibration curves
Seitl, Stanislav; Viszlay, V.
2015 - English
Compact tension (CT) test is in engineering frequently used test for metallic materials to determiner fracture parameters/properties, e.g. fracture energy, fracture toughness, crack propagation rate, J-R curves etc. [20]. The modified compact tension (MCT) specimen for cement based composites has to be prepared due to negligible concentration around the holes for tenons. An accurate determination of fracture parameters requires the use of a valid calibration curves, there for in this contribution the stress analysis near the crack tip and calibration curve for modified compact tension test are introduced. The calibration curve is introduced for diameter 150 mm (the specimen could be easy made from the specimen for compression test) and includes all theoretical imperfections that results from preparation of the MCT specimens. Keywords: Modified compact tension specimen; stress intensity factor; concrete; FEM Available at various institutes of the ASCR
Stress analysis of modified compact tension specimens: K-calibration curves

Compact tension (CT) test is in engineering frequently used test for metallic materials to determiner fracture parameters/properties, e.g. fracture energy, fracture toughness, crack propagation rate, ...

Seitl, Stanislav; Viszlay, V.
Ústav fyziky materiálů, 2015

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